Known from DE 198 21 467 A1 is a one-, two- or multidimensional, difference transmission for high resolution measuring of the number of whole numbered revolutions of a shaft. In the simplest case of the one-dimensional, difference transmission, only two gears are used. These differ as regards tooth count by one tooth. One of the gears is mounted directly on the shaft to be measured and drives the second gear. Based on the angular positions of the two gears relative to one another, the number of revolutions of the shaft can be determined.
Disclosed in DE 198 21 467 A1 is, furthermore, a two-dimensional, difference transmission having three gears, wherein a first gear is again associated with the shaft to be measured, while the two other gears are driven directly and/or indirectly by the first gear. Via the basic combinations, which result for the different number of rotations of the gears and which are possible in the case of defined tooth counts of the individual gears, the number of whole numbered revolutions is ascertained. In order to achieve uniqueness as regards the number of whole numbered revolutions, standardized base values of the basic combinations are calculated for the different numbers of rotations and stored in a two-dimensional array. In such case, the standardized base values serve as memory coordinates, based on which the whole numbered number of rotations can be ascertained. The disadvantage of the known solution is that the resolution lies in the vicinity of one whole numbered revolution. With the known solution, it is not possible currently to determine the exact angular position of the shaft of the measured object.
In connection with actuators, a high resolution, multi-turn, spur gear transmission is known for measuring the absolute rotation angle. In the case of the known spur gear transmission, a number of transmission stages coupled with one another are applied. In the case of a preferred solution of the multi-turn, spur gear transmission, 23 gears and five position sensors are applied. The individual transmission stages must be manufactured with high precision, in order to minimize slack in the individual transmission stages arranged one after the other.